Add skiboot-5.5.0 release notes
Add skiboot-5.5.0 release notes

Signed-off-by: Stewart Smith <ec31ab75ddf977353c8f660f92ea8b23f64aef25@linux.vnet.ibm.com>

shenki/skiboot,legoater/skiboot,shenki/skiboot,qemu/skiboot,shenki/skiboot,shenki/skiboot,legoater/skiboot,qemu/skiboot,qemu/skiboot,shenki/skiboot,legoater/skiboot,open-power/skiboot,open-power/skiboot,legoater/skiboot,open-power/skiboot,legoater/skiboot,stewart-ibm/skiboot,open-power/skiboot,stewart-ibm/skiboot,qemu/skiboot,mikey/skiboot,stewart-ibm/skiboot,open-power/skiboot,qemu/skiboot,mikey/skiboot,mikey/skiboot